544 bepobt — 1884. 



Now the Wrekin volcanic rocks must be distinctly older than the 

 Ordovician ; hence we refer them, to the same set of outbursts as the late 

 Archaean volcanoes of Wales. But there are considerable resemblances 

 between these and the oldest rocks at the Lickey. Hartshill, and the 

 more rhyolitic lavas of Charnwoocl (not to mention resemblances of the 

 ordinary detrital beds), and all these differ markedly from the lavas of 

 the Arenig or Bala beds of Wales. Hence it seems reasonable to suppose 

 that in the latest part of the Archaean period there were nnmerous 

 volcanic outbursts of very similar materials in Britain, and that of these 

 the beds already mentioned are records. 



(C) Scotland. 



(10.) The Highlands. — This mountainous region has for full thirty 

 years been a battle-ground for rival theories, and the war which was so 

 keenly wa<*ed between Murchison and Nicol has now, after a truce of 

 exhaustion rather than of agreement, again broken out. In the limited 

 space of this paper it would be impossible to enter into the details of the 

 controversy, so that it must suffice to give the main outlines of the 

 chief conflicting views. First, as to the points on which the main body 

 of competent observers are agreed. Along the western border of the 

 N.W. Highlands and in the Outer Hebrides, is a great area of metamorphic 

 rock which clearly forms the foundation-stones of the district. This, the 

 Fundamental gneiss, Lewisian gneiss, Hebridean gneiss, &c, of different 

 authors, is clearly a series of great antiquity ; its characteristics recall 

 those of the Lower Laurentian series of America, and the most ancient 

 rocks of Scandinavia, the Alps, Bohemia, we may say of any locality in 

 the world where we seem to touch the records of the dawn of geological 

 history. Its rocks may be described in the words of Dr. A. Geikie, the 

 present head of the Geological Survey of Great Britain : ' They consist of 

 a tough massive gneiss, usually hornblendic, 1 with bands of hornblende- 

 rock, hornblende-schifit, actinolite-schist, eclogite, mica-schist, sericite- 

 schist, and other crystalline rocks. In two or three places they enclose 

 bands of limestone. 2 .... In traversing the western seaboard, from 

 Cape Wrath to Loch Torridon, I have ascertained that these ancient 

 rocks are disposed in several broad anticlinal and synclinal folds, the 

 angles of dip not exceeding 30° to 40°, and the strata succeeding each 

 other with unexpected regularity, though here and there showing great 

 local crumpling. The lower portions of the series are on the whole more 

 massive than the upper, and more traversed by pegmatite veins.' 3 Above 

 this metamorphic series comes a mass of indurated reddish grit, sometimes 

 a conglomerate or breccia, commonly called the Torridon sandstone. This 

 is of very variable thickness ; in the Loch Maree district it is supposed to 

 be 'at least 8,000 feet tliick,' 4 while near Loch Eriboll it is practically 

 absent. It overlies, with gi-eat unconformity, the Hebridean gneiss, and 

 is in turn overlain, it is generally said unconformably, by a group of 

 quartzites, which are succeeded conformably by calcareous beds. It is 

 proved, on the evidence of fossils, that these limestones and the underlying 

 quartzites are of Ordovician age ; hence the ' Torridon sandstone ' is con- 

 sidered to be Cambrian. In apparent succession to the Ordovician lime- 



1 Black mica also is by no means wanting:. — T. G. 13. 



J Highly crystalline, so far as I know. — T. G. B. 



3 Text-book of Geology, p. 640, ed. 1882. ' Geikie, ibid. p. 656. 



